In intelligent devices such as a computer or a mobile terminal, there are many methods for recognizing a user's touch or touch motion in order to control the corresponding device. Currently, the most commonly used methods for recognizing a touch are a pressure-sensitive touch input sensing method and a capacitive touch input sensing method.
The pressure-sensitive touch input sensing method can precisely recognize a contact point, but has disadvantages in that recognition may be achieved only when more than predetermined pressure is applied to the surface of a recognition device, and it is difficult or impossible to apply the method to a flexible material. Korean Patent Application No. 2008-0081417 discloses “Input Detection Method using Piezoresistive Layer”, but when the piezoresistive layer is applied to a flexible material such as fabric, not only touch input but crumpling of fabric affects the piezoresistive layer, which makes it impossible to exactly detect input.
The capacitive touch input sensing method provides good touch feeling, but has a complicated circuit configuration and costs a lot of money. In addition, since the method detects a change in capacitance due to a human body touch, it is difficult to use the method in an area adjacent to a human body such as a smart garment and a wearable computer. Therefore, it is difficult to apply the method to simple operation of a small electronic device by remote control and an input device in the wearable computer.
In recent years, a touch input sensing method using light has been actively studied. U.S. Pat. No. 7,598,949 suggested a method for both displaying graphics and sensing touch input using light that is emitted from an LED and reflected by a finger, by using a light-emitting diode (LED) array. However, the method has a disadvantage in that unnecessary power is consumed in a device that does not need an LED output and illumination of the surrounding environment acts as noise to reduce a touch recognition rate. Korean Patent Application No. 2003-0088542 suggested an input apparatus which can substitute for a button by sensing when a user's touch blocks the light quantity input into a sensor using an illumination sensor. When the illumination sensor is used, a service life can be extended compared to an existing button, and an element is small and thus occupies a small space. However, the application did not suggest a solution to the possibility of occurrence of an erroneous operation in the interior having an insufficient light quantity or under sunlight having a very excessive light quantity.